The present invention relates to glide heads for evaluating the glide quality of a disc surface, and to related methods. More particularly, the invention relates to glide heads that detect collisions of the slider with a defect on a disc surface.
Disc drives are used for storing information, typically as magnetically encoded data, and more recently as optically encoded data, on a disc surface. Glide tests are used to check disc surfaces for defects. Glide tests allow computer disc manufacturers to control and assure the quality of the disc media. Generally, all hard drive discs are tested before shipment. During a glide test, the glide head or slider flies over a disc surface generally at a predetermined clearance from the disc surface, known as the glide height or fly height.
If contact occurs between the glide head and a disc defect or asperity, the glide head detects the contact using various known methods such as vibration or thermal energy detection. The vibrations can be measured with a piezoelectric transducer (PZT), which generates a potential difference between the electrodes of the PZT due to deformation of the transducer. Specifically, when the glide head interacts with a defect on the spinning disc, simultaneously excited vibrational modes of the PZT and the head result in voltages at corresponding frequencies. If the magnitude of measured voltages exceed predetermined threshold values, the disc may be rejected. Contact can also be detected using a magneto-resistive or other sensor which exhibits a change in operation in the presence of thermal energy generated as a result of the contact.
An important requirement upon which the realization of high data recording densities (20 Gb/in2 and beyond) in hard-disc-drive-based data storage systems is the ability to maintain very low head-to-disc separations (i.e., flying eights), for example of 0.5 xcexcin or lower. This inherent requirement has lead to the development of media with ultra low glide heights or, equivalently super-smooth surface finishes with center line average roughness (Ra) in the range of 0.2-0.6 nm.
The glide tests (also called characterization or certification) of media involves the determination, using a xe2x80x9cglide headxe2x80x9d, of the flying height at which head-to-disc contact is first detected. Such flying height is regarded as the media glide height. Typically, head-to-disc contact is induced using xe2x80x9cspin-downxe2x80x9d, or xe2x80x9crotation per minutexe2x80x9d (RPM) drop, as a glide head flies over the media surface to be characterized/certified. Knowledge of the variation of the fly height with RPM for the glide head allows the determination of the glide height.
A glide characterization/certification of super-smooth media using conventional glide heads having smooth air bearing surfaces presents a serious risk In effect, when the two smooth surfaces in relative motion are brought into contact, a large number of contact junctions are formed at the contact interface, resulting in a large real area of contact between the glide head and the media. Under such conditions, the friction force resisting the relative sliding motion between the contacting surfaces is proportional to the large number of contact junctions that must be sheared off if relative motion is to occur. Thus, the contact of a conventional glide head and a super-smooth disc surface can be expected to be accompanied by a large friction force built-up, which can lead to slider forward pitching, air-bearing destabilization, and ultimately, a head crash. This situation effectively limits the usefulness of conventional glide heads for the glide characterization/certification of super-smooth media. Consequently, a new approach of characterizing/certifying super-smooth media is needed.
The present invention includes the realization that air bearing surface (ABS) microtextung (i.e., the production of well-defined texture patterns on an ABS) affords an effective method to control the size of the apparent area of contact during head-to-disc frictional interaction, and thus provides a method to effectively prevent excessive friction force build-up which can lead to catastrophic tribological failure (head crash) during the glide characterization of super-smooth media for high areal density (for example greater than 20 Gb/in2) head-to-disc interfaces (ADIs).